Some dampers used for a suspension of a vehicle include a damping valve configured to change a damping force. As such damper, there has been known the following damper. The damper includes a cylinder, a piston that partitions an inside of the cylinder into an extension-side chamber and a contraction-side chamber, a piston rod whose one end is coupled to the piston and is movably inserted into the cylinder, and damping valves. The damping valves include passages that allow communication between an extension-side chamber and a contraction-side chamber provided in the piston, disc valves that separate from and are seated on ring-shaped valve seats, which surround exit ends of the passages provided in the piston to open and close these passages, back-pressure chambers that cause a pressure led from the extension-side chamber or the contraction-side chamber to act on back surfaces of the disc valves, and electromagnetic pressure control valves using a solenoid to control a pressure in the back-pressure chambers (for example, see JP2001-12530A).
The damper thus configured can control a damping force during extension and contraction by controlling the pressure in the back-pressure chambers by the electromagnetic pressure control valves. However, in a valve-closed state where the disc valves are seated on the valve seats, liquid passes through fixed orifices provided at the disc valves to come and go between the extension-side chamber and the contraction-side chamber. In view of this, when the piston moves at a low speed, the damper mainly provides the damping force by the fixed orifices.